1. Field of the Invention
The present invention relates to a liquid crystal display device (LCD)using flexible films, and a method of producing the same. More particularly, the present invention relates to an LCD which allows, despite a low gas barrier capability, a minimum of bubbles to be produced in liquid crystals intervening between polymer film substrates and distributes, when a spacer is sprayed, the spacer uniformly enough to set up a uniform cell gap, thereby achieving a desirable display characteristic free from noticeable color speckles, coloring, etc. The present invention is also concerned with a method of fabricating such an LCD.
2. Discussion of the Background
Japanese Patent Laid-Open Publication (Kokai) No. 61-15128, for example, proposes an LCD having substrates implemented by polymer films. One of the substrates has high resistivity to heat and liquid crystals while the other substrate has low air permeability. This kind of configuration prevents bubbles from being easily formed in a liquid crystal layer. Let this conventional LCD be referred to as Prior Art 1.
A polymeric spacer substance may be sprayed to between the substrates or polymer films such that it occupies 1% to 30% of the entire display area when projected onto the display area, as proposed in Japanese Patent Laid-Open Publication No. 60-159727 (referred to as Prior Art 2 hereinafter). In this case, the spacer sets up a uniform gap between the substrates to cause a minimum of speckles to occur.
Japanese Patent Laid-Open Publication No. 64-78227 discloses an LCD in which a spacer in the form of true spherical plastic beads, silica beads or alumina beads is sprayed onto polymer film substrates undergone alignment treatment (referred to as Prior Art 3 hereinafter). The spacer has a standard particle size deviation of less than 0.3 .mu.m and a scattering density of 100 particles to 200 particles/mm.sup.2. As a result, the cell gap accuracy is improved to reduce color speckles.
Further, Japanese Patent Laid-Open Publication No. 1-241523 teaches an LCD using substrates also implemented by polymer films, and a spacer whose standard particle size deviation is less than 0.3 .mu.m; the spacer is a mixture of spherical particles scattered at a density of 100 particles to 200 particles/mm.sup.2 and glass fibers scattered at a density of five fibers to thirty fibers/mm.sup.2 (referred to as Prior Art 4). This kind of spacer insures a uniform cell gap and, therefore, reduces color speckles.
Prior Arts 2-4 each implements substrates with polymer films which are more resistive to shocks and impacts than glass substrates. However, the problem with polymer films is that the gas barrier capability is low. When the polymer films are left in a hot and humid environment over a long period of time, gasses sequentially permeate and penetrate the films and dissolve in the liquid crystal layer to produce bubbles. The bubbles to degrade the display are apt characteristic of the LCD.
In light of the above, Prior Art 1 includes means for enhancing the gas barrier property of the substrates. Substrates with gas barrier coatings, e.g., PC (Poly Carbonate) or PAR (Poly Arylate) substrates or PES (Poly Ether Sulfone) substrates having a composite gas barrier film mainly constituted by EVA (Ethyrene Vinyl Acetate copolymer resin) on the top and bottom thereof have air permeability of 1 to 10 m1/m.sup.2 /24 h/atm/20.degree. C. With such substrates having low air permeability, it is possible to reduce bubbles to occur in the liquid crystal layer. However, even these kinds of substrates allow gasses to sequentially permeate them as time elapses and are, therefore, apt to suffer from bubbles. In addition, the gas barrier films formed on the top and bottom of the substrates increases material and production costs.
Another problem with Prior Arts 2-4 is that a charge is apt to deposit on the polymer films or substrates. Particularly, the polymer films are noticeably charged during a rubbing step. When the spacer is sprayed onto such charged substrates, the distribution thereof is not uniform, i.e., it is aggregated at some portions and practically absent at some portions, resulting in a non-uniform cell gap. Hence, considering even an area as small as 1 mm.sup.2, when the spacer distribution is irregular, color speckles occur although the spacer may be deposited in a predetermined amount in such a small area. This is particularly conspicuous when it comes to an STN (Super Twisted Nematic) mode LCD.
Some different approaches, including one taught in Japanese Patent Laid-Open Publication No. 64-88428, are available for dissipating static electricity existing on the surfaces of the substrates to which the spacer is to be sprayed. For example, ionized air may be blown onto the substrates. Even with such is approaches, however, it impossible to fully eliminate the irregular spraying of the spacer.
For conventional spacers, a reference may be made to, for example, U.S. Pat. Nos. 5,029,985, U.S. Ser. No. 233,747 filed Aug. 19, 1988, and U.S. Pat. Nos. 5,067,796 and 5,011,266.